Parasite may have killed Sue, other T. rexes

September 29, 2009

Sue, the biggest, meanest meat-eating dinosaur known to history, probably was killed not by some other monster killer battling with her 65 million years ago, but by a tiny one-celled parasite that gave her a killer sore throat.

That is the conclusion drawn by an international team of scientists who studied holes in the jaw of Sue, the biggest, most compete Tyrannosaurus rex fossil ever found and one of the star attractions at the Field Museum.

The holes in Sue's mandible bones at one time were thought to be bite marks by another T. rex during a fight sometime during her life. A paper published Tuesday in the online science journal PLoS ONE says instead that the holes were made a parastic infection called trichomonosis, which continues to cause fatal disease in modern-day carnivorous birds known as raptors -- hawks, eagles and osprey.

"The general idea is that if a tyrannosaur had this infection, and you see holes in the mandibles, it would mean the animal had a really serious infection in the back of the throat, making it very difficult to feed and breathe," said Ewan Wolff, a paleontologist at the University of Wisconsin who is the lead author of the article.

"We see modern birds of prey succumb to this disease," said Wolff, who has a PhD in paleontology and is now in his third year in veterinary medical school.

He and three other paleontologists, Steven Salisbury, University of Queensland, Australia, and Jack Horner at and David Varricchio Montana State University, studied the jaws of 65 fossil tyrannosaurs, finding 10 of them that had similar holes in their jaws. The disease evidence was found in other T. rex fossils, and also in fossil tyrannosaur species that lived slightly earlier than T. rex, daspletosaurus and albertosaurus.

Modern birds of prey suffer from trichomonosis caused by a protozoan parasite called Trichomonas gallinae, Wolff said. It causes lesions in their jawbones, and the pattern of those holes closely match those found in tyrannosaur mandibles both in appearance and shape.

The holes do not have the appearance of more obvious puncture wounds left by the teeth of other animals in other fossil tyrannosaurs, the paper's authors said.

The suspected culprit parasite, Wolff said, "is a protozoan, a single-celled organism" that in mammals like humans and cattle is a sexually transmitted disease, but in birds of prey and -- probably -- in tyrannosaurs is spread by eating the infected flesh of their prey.

"It appears from the lesions in Sue that she was in a pretty advanced stage of the disease," said Wolff. "It may have been the cause of her death."